It is often desirable to take x-rays of a patient from a number of different positions, preferably without the need for frequent manual repositioning of the patient of the x-ray system. Mobile C-arm x-ray diagnostic equipment has been developed for this purpose, and has become well known in the medical art of surgical and other interventional procedures.
A C-arm refers generally to an elongated C-shaped member terminating in opposing distal ends of the “C” shape. An x-ray source and an image receptor are typically mounted at or near the distal ends, respectively, of the C-arm in opposing orientation, with the C-arm supported in a suspended position. The space within the C-shape of the arm provides room for the physician to attend to the patient substantially free of interference from the x-ray support structure. The support structure usually rests upon wheels, which enable the C-arm to be wheeled from room to room, also to move along the length of a patient while the physician operates or examines. The x-ray images from such devices are often used in the operating room environment to help ensure that devices such as surgical instrumentation are properly positioned during the procedure.
The C-arm is usually mounted so as to enable rotational movement of the arm in two degrees of freedom, i.e. about two perpendicular axes in a spherical motion. More specifically, the C-arm is slidably mounted to the support structure to enable orbiting rotational movement of the C-arm about its center of curvature, thereby permitting selective orientation of the x-ray source and the image receptor vertically, horizontally, or somewhere in between. The C-arm is also laterally rotatable, i.e. in a perpendicular direction relative to the orbiting direction to enable selectively adjustable positioning of the x-ray source and receptor relative to both the width and length of the patient. The spherically rotational aspects of C-arm apparatus allows the physician to take x-rays of the patient at an optimal angle as determined with respect to the particular anatomical condition being imaged. An example of such a C-arm apparatus is described in U.S. Pat. No. 4,955,046 to Siczek, et al., which discloses a C-arm apparatus on a wheeled support cart.
In many cases, it is desirable to obtain x-ray images of a patient from multiple projection planes, preferably in quick succession and without repositioning the C-arm. Such a configuration is often referred to as bi-planar imaging and allows an object to be viewed in two planes simultaneously. The two x-ray beams emitted from the two x-ray tubes may cross at an iso-center. Bi-planar imaging is useful for checking of a catheter position, a balloon status or performing a digital subtraction run.
Bi-planar imaging may be accomplished in several ways. One way is by using two independent imaging systems, or two C-arms. U.S. Pat. No. 4,884,293 to Koyama discusses a dual imaging system with one imaging system being mounted to the floor and the other being mounted to the ceiling. One disadvantage of this system is that it is permanently mounted to the floor and ceiling. Thus, the system cannot be moved about a hospital as needed. Another disadvantage of this system is that, although the C-arms are coordinated, the imaging systems operate independently of one another. Thus, the images produced are not coordinated.
Another configuration for obtaining bi-planar imaging is slidingly nesting one C-arm in another. U.S. Pat. No. 5,515,416 to Siczek et al. describes a dual imaging system with one C-arm being mounted to the floor and the other C-arm being slidingly disposed on the first C-arm. One disadvantage of this system is that the two imaging systems may not be moved independently of one another. Thus, the positioning of the second imaging system is limited by the position of the first. Another disadvantage is that the dual x-ray system is permanently mounted to the floor. Thus, it cannot be moved about a hospital. A further disadvantage is that the two images must share a common iso-center because they are nested.
Yet another configuration for obtaining bi-planar imaging is disposing the imaging systems in a ring, as opposed to C-arms. U.S. Pat. No. 3,549,885 to Andersson discloses a dual imaging system with both imaging systems being mounted perpendicularly in a rotatable ring. One disadvantage with this system is that the bi-planar images are always disposed at a fixed, perpendicular angle with respect to each other.
Still another configuration for obtaining bi-planar imaging is disposing the imaging systems on a G-arm, as opposed to C-arms. U.S. Pat. No. 5,095,501 to Kobayashi discloses a dual imaging system with both imaging systems being mounted perpendicularly in a G-shaped arm. Like the ring configuration above, one disadvantage of this system is that the bi-planar images are always disposed at a fixed, perpendicular angle with respect to each other.
Furthermore, it is often desirable to view x-rays in real time and to save or store x-rays taken of a patient for later review. Dual imaging systems are complicated and difficult to operate because they require simultaneous coordination and operation of two independent and distinct imaging systems. In addition, if both imaging systems operate at the same time, the two x-ray beams interact to cause a blurred image. Moreover, the use of two x-ray sources can result in exposure of the subject to excessive radiation, particularly due to scattering effects. To date, there does not exist an electromagnetic radiation imaging system that employs a single source to provide simultaneous or near-simultaneous acquisition of object images from multiple projection planes.